A defibrillator is an electronic device that applies a short high voltage pulse to the heart by means of electrodes placed on the chest wall. It is used to restore a more desirable rhythm to a heart experiencing ventricular fibrillation, ventricular tachycardia, or other abnormal heartbeat patterns. Ventricular fibrillation is rapid erratic contractions of the muscle fibers of the ventricles that do not result in coordinated contractions of the ventricles. Ventricular tachycardia is an abnormally rapid heartbeat generated by excitation within the ventricles.
To determine if defibrillation is required, most defibrillators have, in the past, relied on manual interpretation of ECG signals displayed on an ECG monitor or plotted on a strip of paper. In such systems, the ECG signal is displayed as a waveform normally containing the P and T waves, as well as the QRS peaks associated with ventricular contraction. The operator interprets the sometimes noisy waveform to determine the presence of ventricular fibrillation, ventricular tachycardia, asystole (the absence of contractions of the heart), or other abnormal heartbeat patterns. The operator must be highly trained in order to manually interpret the ECG signals with the degree of accuracy necessary to base a decision to defibrillate on his or her interpretation. Manual ECG interpretation has thus worked adequately in hospitals where equipment and trained personnel are readily available. Increasingly, however, defibrillators are being used outside the hospital by relatively untrained individuals such as paramedics, emergency medical technicians, firemen, policemen, and other individuals who respond to an emergency on the scene.
The recently introduced automatic and semiautomatic defibrillators eliminate the requirement of manual ECG interpretation by having microprocessors or other electronic hardware perform the ECG interpretation. An automatic defibrillator interprets ECG signals, makes a decision whether to treat (defibrillate) a patient, and then, when the decision is to treat, automatically defibrillates the patient. A semiautomatic defibrillator interprets ECG signals and makes the decision whether to treat the patient, but then presents the decision on a display or other means to an operator. The operator then initiates the defibrillation according to the decision.